In Defence of Bill Bennett III this time it's personal
I agree with Matthew Yglesias (but question his choice of words in the post above)
"Not only is Bennett clearly not advocating a campaign of genocidal abortion against African-Americans, but the empirical claim here is unambiguously true. "
Garance Franke-Ruta claims that Bennett's positive assertion (claim about conditional probabilities) might be false. This criticism is true, but it is based on ignoring context. The caller made a conditional forecast using a simple static model in which it is assumed that employment rates and pregnancy rates don't change dramatically given changes in abortion. The caller said that the social security shortfall would not exist if abortion had been banned. He assumed that a ban on abortion would not affect pregnancy and that the resulting counterfactually increased population would have the same employment rate as the actual population. In a later post, Yglesias notes that these positive claims are probably false. Women who abort are more likely to reproduce than otherwise similar women who do not abort, thus, it is possible and even seems true that abortion affects the timing but not the number of births.
In his reply, Bennett used a similarly crude positive analysis assuming, for the sake of argument, that future crime could be predicted using crime rates. The resulting argument is not just morally absurd (as intended) it is also a very crude and unconvincing conditional prediction (as noted by Garance Franke-Ruta) just like the argument made by the caller. I think it is very natural to believe that Bennett was deliberately imitating and parodying the extreme crudeness of the approach to forecasting as well as the moral blindness of the caller. He would have made his point clearer and been less offensive if he had said "you could just as well argue that" then continued. He was live on radio (note Brad warns not to try a reductio ad absurdam on talk radio because one can't check and edit ones words when on the air live). Also the clause which I suggest is clearly implicit given the context.
update: I found the link and replaced "???" with "Garance Franke-Ruta".